#3 What is the reason or advantage for Pitchers to throw from a (pitchers) mound?#4 The "Infield Fly Rule" was implemented in order to prevent what from happening?#5 Where does the 7th Inning Stretch originate from?

In a baseball game, when a pitcher strikes out a batter, you'll see K's on the scoreboard and fans holding K signs along the hand railing for each strikeout.#1 What is the significance of the letter K?#2 What is the significance of the backwards K?